Obesity and its associated diseases are the leading causes of mortality in the Unites States. Insulin resistance and type 2 diabetes mellitus are two pathological conditions with strong correlations to obesity. It has been established that insulin resistance is temporally associated with chronic adipose tissue inflammation;this inflammation is believed to be primarily associated with macrophage and lymphocyte recruitment to adipose tissue. To date, there is a lack of understanding on what initiates this inflammatory response and more importantly there are no safe and effective therapies to reverse the progression of this disease. The proposed research will investigate a mostly unexplored area in this field, investigating the effects of the complement system, specifically complement factor 5, on adipose tissue inflammation and insulin resistance. The overall goal of this project is to provide mechanistic insight into the specific roles of the complement 5 cleavage products, C5a and C5b, in adipose tissue physiology. This knowledge could lead to the development of therapies against insulin resistance and type 2 diabetes. The first aim of the proposed project will investigate the effects of C5 deficiency on adipose tissue inflammation and systemic insulin sensitivity. C5-/- and wild-type (WT) mice will be purchased from the Jackson Laboratories and placed on a high fat diet for 16 weeks. After this period differences in insulin sensitivity will be assessed by glucose and insulin tolerance tests as well as hyperinsulinemic- euglycemic clamps. Adipose tissue inflammation will be assessed using three different approaches: 1) mRNA expression of inflammatory molecules in total epididymal adipose tissue by real-time RTPCR. 2) Inflammatory protein levels in total epididymal adipose tissue by western blot analysis, immunofluorescence and immunohistochemistry. 3) The number of inflammatory immune cells present in the stromal vascular fraction of epididymal adipose tissue. The second aim of this project will discern the roles of C5a versus C5b in adipose tissue inflammation and insulin resistance;in addition, it will test the reversal of the progression of this disease by blocking the action of these molecules. In this study, WT mice will be placed on a high fat diet for 8 weeks to induce insulin resistance. After this period mice will be divided into four treatment groups: anti-C5a serum, anti-C5b serum, IgG control, or no treatment. The mice will be injected with the antibodies twice a week for 4 weeks while they are sustained on the high fat diet. At the end of this period insulin sensitivity and adipose tissue inflammation will be evaluated as described in aim 1. It is expected that both the anti-C5a and anti-C5b treatments will reduce inflammation and improve insulin sensitivity. PUBLIC HEALTH RELEVANCE: The proposed research will investigate an important component of the immune system and its involvement in inflammation of abdominal fat tissue. Inflammation of fat tissue has been shown to be associated with insulin resistance and type 2 diabetes. Thus, understanding the mechanism by which the immune system promotes this inflammation could help develop new therapies against these diseases.